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Ok, thanks for the info. I was just making sure a device doesn't exist like a special switch that could do the same. But I can make it work if I need to. Using single wires to plug power and ground works the easiest but my supplier has 0 JST single plug housings as they are on back order. No rush, I will possibly just back order some for future reference.

Dave

On 11/13/2020 6:14 PM, Harvey White wrote:

If the connector is keyed, and you really can't plug it in backwards, then you don't need symmetric pins. Some connectors can be forced in backwards.

There are keys that fit into the connector in place of a socket. The mating pin needs to be removed.? I might try to 3D print some of them, but the best solution might be to go to a hobby shop and get some very thin plastic that could fit into the connector from the back to block the pin being inserted.

I've tried finding them, but they seem to be rather expensive, where they are available.

So for connectors where the body is not keyed, you need to key the pins if it's important.? Another method would be to put power and ground in such locations that plugging the connector in backwards doesn't connect nasty signals (like outputs to outputs), power to ground, etc.? This takes some careful work and may not always be possible.

The symmetric method is workable, and you may end up thinking of 3D printing your own shrouds for the on board pins to keep the plug from being inserted off by a pin (or just key it).

Harvey


On 11/13/2020 6:18 PM, Dave wrote:

Thanks Harvey. It all makes perfect sense now that I remembered the VIA. One bonus round question. What if you wanted to reverse the polarity and you had a connector ( 2 pin ) that was "keyed" so you couldn't just unplug and re-plug it in the opposite way? Like with a JST XH series. I know with a standard 0.1 header pins that wouldn't be a problem but are there any tricks to make that happen? Just curious because us noobs ask the strangest questions and sometimes they are good ones.

Thanks,

Dave

On 11/13/2020 4:46 PM, Harvey White wrote:

yet more replies.....

On 11/13/2020 3:42 PM, Dave wrote:

Interleaved some more.

On 11/13/2020 12:53 PM, Harvey White wrote:

Interleaved.

On 11/13/2020 1:11 PM, Dave wrote:

Harvey,

? I have a related question here after spending some time researching. I already have a bunch of JST XH connectors and plugs, and pins and the crimper.

Instead of JST, I use 0.1 inch spacing connectors.? The female/female jumpers can be tweaked to remove the individual shrouds, and can be reinserted in strip connectors to make some decent cables.? JST will work fine, but I've found them tricky to use.? I'd just as soon look for premade cables. Your luck with the crimper (I hope) will be better than mine.

??????????? The .1 inch (2.54mm) spacing should work ok with the JST 2.5mm spacing, at least for short length stuff. SO I should be good there. I did look at premade cables but noticed nobody bragging about 100% copper and after researching deeper found most use copper clad aluminum. I hate that stuff as I need to cut the cables and solder one end elsewhere. I have had good enough luck with the JST crimping but have another crimper on my list to order.

It's ok.? You just don't want to mix the 2 mm and 2.54 mm stuff. I generally use 0.1 inch spacing because that's easy to find. The 2.0 mm(or less) JST I use where someone else used it.

I wanted to design a total SMT pcb and I could solder the power and ground wires to a pad. Then I thought about adding a JST header and use a plug for power and ground.

That works.

??????????? Except I don't have any SMT headers in JST XH and although they are available, they come in a 3 circuit style and a 4 and a 5. I really only wanted a 2 circuit version but I have that in a through hole and its also a 90 degree version to save some space on the enclosure height,.

Ok, here's a trick.? I use 5.0 volts as a bulk supply and on each board, typically regulate it to 3.3 volts (this is mostly microprocessor stuff and 3.3 volt modules.? I use 3 pin power connectors (in red) with the inner pin being ground and the outer two pins being +5.? You can't reverse polarity the board except by getting the connector one pin off.

I use through hole connectors.? It doesn't do anything bad except to eat up a little board space.? Remember that on a 90 degree connector, you trade off width for height, and it can make a difference.

Where possible, I make some of the connections symmetric like that.? It costs extra pins, but saves some problems.

Problem is, the JST parts are all through hole. So now for my question ( I may have a clue but will ask anyhow to verify ), what is the best method on the board design to use through hole and SMT at the same time?

I just put them in and let the router do its work.? For your design, you might want to have separate power pins if the supplies are different, say that if you need +5 for the top circuit and +12 for the lower one, have a power connector with separate pins for the two supplies.? That keeps the power supplies from being mixed.

??????????? I guess I was worried about the power feeding the top side while being soldered to the bottom side. I figured I had to have a jumper from the bottom back to the top but now that I think of it, the holes would be plated thru holes...

The holes are plated through holes.? Using EAGLE, for instance, you route on the top layer, then change to the bottom layer, you'll see the trace turn blue and a via put in at the last place the trace stopped.? Continue to route on the bottom of the board, and change layers again to get back to the top layer. Since you don't mount boards directly on a conductive metal plate, it shouldn't matter if there is live power on the other side of the board.? That would be normal for any board.

Using the example where you have absolutely no connections between board sides, if you had a single power connector, the top and bottom grounds and power (if the same voltage) would be connected at the through holes on the connector.

Will I still be able to do my planned 2 different circuits on either side of the board? How should I handle the power header? Use it to supply both sides of the board with one header or use 2 headers for power/GND and separate the copper with islands?

?Given a common ground for both circuits (which works), you're running separate supplies from separate pins, so just one connector and wire it appropriately depending on which circuit you're doing.? You can use unused parts of the other side as jumpers.? If you don't want to do that, you can use 0 ohm resistors (1206 works best just because of the size). it's easier than running wire jumpers.

So yes, one power/signal connector can do the job if you think that the inputs/outputs don't make for too large a connector

If you have a lot of inputs and outputs, there's two ways to do this:

one is to have a separate power connector (and have separate pins for each supply rather than one "power" pin), and then separate connectors for each circuit. I'd use different size connectors to avoid misconnections.

two is to have power and signals on one connector (perhaps few pins for signals) not sharing any pins except ground and identical power supply voltages.

??????????? I didn't even know they made "0" ohm resistors. But I am starting to understand it now. I guess I will start to design it and then in the software things will become obvious.

I think so.? EAGLE's autorouter makes assumptions with their standard setups that are good for having the boards manufactured, but not good for things like toner transfer boards (10/10; 10 mil traces and 10 mil spacing between conductors are workable).? If you're making boards, you need one setup.? If you're having boards made, then use their recommended setups and you're fine.

This is likely true with any other layout program.? Your PCB layout program will automatically (or should) insert a via when you change layers.

Harvey

Thanks,

Dave

Harvey

Thanks,

Dave